Simple technologies for on-farm composting of cattle slurry solid fraction

Composting technologies and control systems have reached an advanced stage of development, but these are too complex and expensive for most agricultural practitioners for treating livestock slurries. The development of simple, but robust and cost-effective techniques for composting animal slurries is therefore required to realise the potential benefits of waste sanitation and soil improvement associated with composted livestock manures. Cattle slurry solid fraction (SF) was collected at the rates of 4 m3 h−1 and 1 m3 h−1 and composted in tall (1.7 m) and short (1.2 m) static piles, to evaluate the physicochemical characteristics and nutrient dynamics of SF during composting without addition of bulking agent materials, and without turning or water addition. Highest maximum temperatures (62–64 °C) were measured in tall piles compared to short piles (52 °C). However, maximum rates of organic matter (OM) destruction were observed at mesophilic temperature ranges in short piles, compared to tall piles, whereas thermophilic temperatures in tall piles maximised sanitation and enhanced moisture reduction. Final OM losses were within the range of 520–660 g kg−1 dry solids and the net loss of OM significantly (P < 0.001) increased nutrient concentrations during the composting period. An advanced degree of stabilization of the SF was indicated by low final pile temperatures and C/N ratio, low concentrations of NH4+ and increased concentrations of NO3- in SF composts. The results indicated that minimum intervention composting of SF in static piles over 168 days can produce agronomically effective organic soil amendments containing significant amounts of OM (772–856 g kg−1) and plant nutrients. The implications of a minimal intervention management approach to composting SF on compost pathogen reduction are discussed and possible measures to improve sanitation are suggested.

► Simple management techniques were examined for composting slurry solid fraction.
► Composting slurry solids was effective without bulking agents, turning or rewetting.
► Maximum rates of organic matter destruction were observed in short piles.
► Thermophilic temperatures in tall piles maximised sanitation and moisture reduction.
► The simple compost management approach maximised N retention and agronomic value.